The present invention relates to an optical pickup for an optical disc player for reproducing information recorded on a disc, and more particularly to a system for controlling the position of an objective of the pickup.
In an optical disc player, in order to read accurately information on a disc, it is necessary to perform a focus control for correcting deflection of the distance between an objective and a tracking position of the disc due to warp and vibration of the disc and a tracking control for controlling the objective so as to follow the track. Therefore, it is necessary to provide driving devices for driving the objective in the focus direction and the tracking direction, respectively.
FIGS. 13 and 14 show a conventional optical pickup. A yoke base 10 made of magnetic material has a pair of inner yokes 10a and a pair of outer yokes 10b. A magnet 11 is secured to an inner portion of each outer yoke 10b. Thus, a magnetic circuit is formed between the magnets.
A printed circuit board 8 having a plurality of leads 12 is secured to one of the outer yokes 10b by a screw 9.
A holder 2 for holding an objective 1 is suspended from the printed circuit board 8 by four metallic wires 6 in the form of a cantilever. Each wire 6 is covered by a rubber tube 5. The holder 2 is disposed in the yoke base 10 and slidably engaged with the inner yokes 10a. The holder 2 has a focus coil 3 wound in the horizontal direction. A pair of tracking coils 4 each of which has a pair of D-shaped coils are secured to both sides of the focus coil 3.
A printed circuit board 7 is secured to the holder 2. Ends of the metallic wires 6 are inserted into holes 2a formed on the holder 2 and soldered to the printed circuit board 7. Both ends of each of the focus coil 3 and the tracking coils 4 are soldered to the printed circuit board 7 and electrically connected to the ends of the metallic wires 6 through copper foils.
When the leads 12 are connected to a source, current flows to the focus coil 3 and the tracking coils 4 through the wires 6. The focusing and tracking of the holder 2 having the objective 1 is controlled in accordance with an electromagnetic operation of the magnets 11.
In the pickup, the tracking coil 4 is secured to the focus coil 3. Accordingly, as shown in FIG. 15, the focus coil 3 and the tracking coil 4 occupy a large space, thereby increasing the magnetic gap formed between the inner yoke 10a and the magnet 11. Consequently, the density of magnetic flux becomes low, so that the magnetic efficiency is low.
Since the magnetic flux actuates perpendicular to the tracking coil 4, it is impossible to reduce a lateral width of the inner yoke 10a. Accordingly, the size of the holder 2 can not be reduced, thereby preventing the size of the pickup from reducing.
Furthermore, since the tracking coil 4 is secured to the sides of the focus coil 3, it is difficult to automatically wind the coils on the holder.